CMP point of use filtration

ABSTRACT

A system for detecting the usable state of a point of use filter of a chemical mechanical polishing (CMP) tool. The system measures the pressure differential across the point of use filter. In one example, the system includes an upstream and a down stream pressure transducer for measuring the pressure differential. The system can provide an indication that the usable state of filter has decreased to a point where the filter needs to be replaced. Such an indication may be displayed on a display located on the polishing tool frame.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates in general to chemical mechanical polishing (CMP) for semiconductor wafers and specifically to the filtration of slurry in CMP.

[0003] 2. Description of the Related Art

[0004] Chemical mechanical polishing (CMP) is commonly used in semiconductor device fabrication for the planarization of structures on a semiconductor wafer. During CMP, a wafer surface is applied to a polishing pad of a polishing tool for planarization of the structures on the wafer surface. Typically, a slurry is applied to the pad during polishing. The slurry typically contains abrasives and/or chemicals which mechanically and/or chemically aid in the polishing of the wafer by the pad.

[0005] With CMP polishing tools, it may be important to limit the particle size of the abrasives in the slurry. Relatively large particles can cause scratches on the wafer, thereby reducing wafer yields. In addition to causing scratches on the wafers, the relatively larger particles can be more easily “sheared” by devices in the slurry pathway such as e.g. by valves or pumps or by the interior sides of the tubing carrying the slurry.

[0006] Point of use filtering can be implemented in a polishing tool to reduce wafer defects. Point of use filtering involves placing a filter in the slurry pathway between its point of application to the pad and a flow regulator used to regulate the flow rate of slurry applied to the pad during polishing. However, the addition of a point of use filter can increase the maintenance down time due to filter replacement or filter failure.

[0007] What is needed is an improved system for CMP that reduces wafer defects yet minimizes maintenance down time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

[0009]FIG. 1 is a partial perspective view of an embodiment of a CMP polishing tool according to the present invention.

[0010]FIG. 2 is a partial side view of an embodiment of a CMP polishing tool showing components of a point of use filtration system according to the present invention.

[0011]FIG. 3 is a fluid schematic of an embodiment of a slurry delivery system of a CMP polishing tool according to the present invention.

[0012]FIG. 4 is a top view of an embodiment of filter brackets according to the present invention.

[0013]FIG. 5 is a partial side view of an embodiment of a portion of a CMP polishing tool according to the present invention.

[0014] The use of the same reference symbols in different drawings indicates identical items unless otherwise noted.

DETAILED DESCRIPTION

[0015] The following sets forth a detailed description of a mode for carrying out the invention. The description is intended to be illustrative of the invention and should not be taken to be limiting.

[0016]FIG. 1 is a perspective view of a CMP polishing tool 100 that includes a point of use filtration system. Polishing tool 100 is housed in a frame 101. Frame 101 includes a processing compartment 106. Platens, pads, and wafer holders (see items 505, 504, and 510 of FIG. 5) for CMP of semiconductor wafers are located in compartment 106.

[0017] Polishing tool 100 includes a point of use filtering system which measures the pressure differential across a point of use filter to determine the usable state of the filter. In the embodiment of FIG. 1, the point of use filters 249, 250, and 251 are located in filter compartment 125 of frame 101. In the embodiment of FIG. 1, filter compartment 125 includes a transparent door. Locating point of use filters in a compartment of the frame may advantageously allow the filters to be located as close to the platens as possible and may allow the tool to take up less space in a wafer fabrication area. Furthermore, making the filters accessible from the outside of the polishing tool may advantageously ease the change out of the filters.

[0018] Pressure transducers (e.g. 205 in FIG. 2), which are used to measure the pressure at the ends of the filters, are mounted in compartment 103 of frame 101 behind compartment door 128. The filter system also includes bypass valves (e.g. 243 in FIG. 2) located in compartment 130 of frame 100 behind compartment door 132. Also located on frame 101 are display devices (e.g. 115) which include a display (e.g., 116) for displaying information regarding the point of use filters. In one example, display devices (e.g. 115) are D80 dual channel display devices sold by NT INTERNATIONAL of Minneapolis Minn.

[0019]FIG. 2 is a partial side view of polishing tool 100. Point of use filters 249, 250, and 251 are retained in brackets 261 and 263 of filter compartment 125. Filters 249, 250, or 251 can be removed for replacement from the exterior of tool frame 101 via the transparent compartment door of compartment 125. In one example filters 249, 250, and 251 are sold under the trade name STARKLEEN CAPSULE by the PALL Corp. Also located in compartment 125 are isolation valves (e.g. 245 and 253) for isolating the point of use filters (e.g. 249) from the slurry pathway. Tubing (e.g. 259) for the filters and valves passes through back wall 265 of compartment 125 to other components of polishing tool 100.

[0020] Located in compartment 103 (behind door 128 as shown by the cutaway view in FIG. 2) are three sets of pressure transducers (transducers 205 and 207, transducers 211 and 213, and transducers 218 and 220) with each set used for measuring the pressure differential across one of filters 249, 250, or 251. In one example, the pressure transducers are Model 4210 pressure transducers sold by the NT INTERNATIONAL of Minneapolis Minn. However, in other embodiments, other types of pressure sensors such as other types of pressure transducers may be utilized. Three isolation valves (e.g. 243) are located in compartment 130 (behind door 132 as shown by the cutaway view in FIG. 2). In one embodiment, compartments 103, 130 and 125 are made from plastic polypropylene panels hot air welded together. The resulting structure is then attached to other structures of frame 101.

[0021]FIG. 3 is a fluid schematic diagram of a portion of a slurry delivery system of polishing tool 100. The slurry enters the system from a chemical distribution unit (not shown) via a slurry input 325 and is applied via the dispense arms (e.g. 305) to polishing pads (not shown on FIG. 3) located in process compartment 106. From input 325, the slurry flows to an input manifold 311 via pneumatic valves 324 and 326. Peristaltic pumps (e.g. 307) serve as flow regulators to control the flow rate of slurry from input manifold 311 to each of the polishing pads (not shown in FIG. 3) via the dispense arms (e.g. 305). Other embodiments may utilize other types of flow regulators to control the flow rate of slurry such as e.g. other types of pumps, flow meters, or variably controllable valves. A control valve (e.g. 309) is located down stream of each of the pumps (e.g. 307) and can be used for stopping the flow of slurry to a pad or for cleaning input manifold 311 with deionized (D.I.) water. During such cleaning, the valves (e.g. 309) are placed in a position to direct the D.I. water from the pumps (e.g. 307) to the slurry return 327.

[0022] A point of use filter (e.g. 249, 250, or 251) is located down stream of the each of the peristaltic pumps (e.g. 309) in the slurry path to provide point of use filtering for the slurry. For example, filter 249 is located downstream of pump 307. Providing point of use filtering of the slurry may advantageously reduce the number of wafer defects and micro scratches due to large particles in the slurry without changing the polishing performance of the polishing tool. Locating the filter down stream of the flow regulator also filters out particles damaged by the flow regulator (e.g. from particle sheering).

[0023] Over time, a point of use filter clogs up, thereby decreasing the efficiency of the filter. Furthermore, a clogged filter may block slurry flow to the pad, thereby damaging the wafers being polished. Under such conditions, the usable state of the point of use filter decreases to a state where the filter needs to be replaced.

[0024] To provide an indication of the usable state of a point of use filter, polishing tool 100 includes devices for measuring the pressure differential across the filter, which is indicative of the usable state of the filter. As the filter loads or becomes more clogged, the pressure differential across the filter increases. Accordingly, when the pressure differential across the filter reaches a predetermined threshold, an indication is made to an operator that the usable state of the filter is such that it needs to be replaced. In one embodiment, for filters sold under the trade name STARKLEEN CAPSULE by the PALL Corp. having a model number DFA2A015F64, a pressure differential of 3.5 PSI could be used as a threshold to indicate filter replacement.

[0025] In the embodiment shown in FIG. 3, polishing tool 100 includes a pressure transducer located upstream of each point of use filter to measure the pressure at that location and a transducer located down stream of the filter to measure the pressure at that location. For example in FIG. 3, transducer 218 is located upstream of filter 249 and transducer 220 is located downstream of filter 249. Display device 115 is operatively coupled to both transducers 218 and 220 to receive indications from both transducer 218 and 220 of the pressure measured at each transducer. Each of the display devices (e.g. 115) includes a display (e.g. 116) and a controller (e.g. 371) for calculating the pressure differential across the point of use filter and for comparing that calculated pressure differential with a threshold pressure. In one embodiment, controller 371 is implemented with a microcontroller. In other embodiments, controller 371 may be implemented with analog circuitry. In response to a determination that the calculated pressure differential exceeds a predetermined threshold, display device 115 may provides a visual alarm (and/or audio alarm in some embodiments) indicating that the usable state of the filter has reach a point where the filter needs to be replaced. Display device 115 can also, in some embodiments, be configured to display the upstream pressure, the down stream pressure, or the pressure differential. In other embodiments, display device 115 is configured to display the usable state of a filter as a percentage with e.g. 100% indicating a new filter and 0% indicating a filter that needs to be replaced.

[0026] Measuring the pressure differential across a point of use filter to detect the usable state of the filter may advantageously allow a user to replace point of use filters only on an “as needed” basis, as opposed to relying upon an arbitrary measure of the usable state (e.g. time of use or number of wafers polished) for filter replacement. Consequently, the downtime due to point of use filter replacement may be reduced. Further, measuring the pressure differential across a point of use filter may also provide an indication of a premature filter failure. Such an indication may be used to reduce the consumable cost of wafer manufacturing due to a reduction in damage to wafers in progress. In addition, such a system may be used to provide a warning that the usable state of a point of use filter is approaching a level where the filter needs replacement, thereby giving maintenance adequate time to ensure that a replacement filter is available when needed. Accordingly, a system utilizing pressure differential measurement to indicate the usable state of a point of use filter may advantageously allow a system to realize the advantages of point of use filtering while minimizing the disadvantages of an added filtering system.

[0027] Referring back to FIG. 3, polishing tool 100 includes an a system controller 343 that is coupled to each of the display devices (e.g. 115) in a wired-or configuration to receive an alarm indication that the usable state of a point of use filter is such that the filter needs to be replaced. Controller 343 causes this alarm condition to be displayed on display 339 and also causes the initiation of an audio alarm of this condition as well. In other embodiments, controller 343 receives an indication of the measured pressure differential from each of the display devices (e.g. 115), wherein controller 343 causes the display of the pressure differential of each filter on display monitor 339. In one embodiment, controller 343 is programmed with a predetermined threshold pressure. Controller 343 would cause an alarm to be displayed on display 339 if controller 343 determines that the pressure differential measurements received from any the display devices (e.g. 115) exceeds the threshold.

[0028] The slurry pathway to each polishing pad (not shown in FIG. 3) also includes a bypass valve e.g. 243 for allowing for the bypass of the point of use filter during a polishing operation or a cleaning operation. The bypass valves may also be used for trouble shooting the system to determine whether the point of use filters are functioning properly. During the utilization of a point of use filter (e.g. 249), the bypass valve (e.g. 243) corresponding to that filter is placed in a closed position. Also, during the utilization of a point of use filter, the isolation valves corresponding to the filter (e.g. valves 253 and 245 correspond to filter 249 in FIG. 3) are placed in an open position. The isolation valves are placed in a closed position during a cleaning operation, during the bypass of the point of use filter in conjunction with the bypass valve (e.g. 243), or during change out of the point of use filters.

[0029] In one example, point of use filters 249, 250, and 251, the upstream and downstream pressure transducers (e.g. 218 and 220), the upstream and downstream isolation valves (e.g. 253 and 245), the display devices (e.g. 115), and the bypass valves (e.g. 243) are implemented in a MIRRA polishing tool sold by APPLIED MATERIALS. However, those of skill in the art will recognize that, based upon the teachings herein, a point of use filter system with pressure differential measuring may be implemented in other types of polishing tools.

[0030] Referring back to FIG. 2, filters 249, 250, and 251 are retained in brackets 261 and 263 of component 125. FIG. 4 shows a top view of brackets 261 and 263. In one embodiment, brackets 261 and 263 are made from ⅜″ white polypropylene. In one embodiment, the brackets are hot air welded to the walls of compartment 125.

[0031] Brackets 261 and 263 each include three semi-circuit notches (e.g. 415) sized to hold the point of use filters (e.g. 249). The notches are sized according to the diameter of a filter at the location where the filter fits into the notch. In the embodiment shown, the notches of upper bracket 261 have a slightly smaller diameter (2.53″) than the diameter (2.63″) of the notches of lower bracket 263.

[0032] The notches extend into brackets 261 and 263 by 1.50″, which is greater than the radius of the notches (a 1.265″ radius for the notches of bracket 261 and a 1.315″ radius for the notches of bracket 263). Accordingly, when a filter is installed in brackets 261 and 263, the edges of the notches extend around the filter by greater than 180 degrees. To install or remove a filter from a bracket, the ends (e.g. 465) of the bracket notch edges have to be pushed slightly apart by the filter, providing for a snap-in effect during installation and providing for a retention force to hold the filter in place. Accordingly, for the embodiment shown, the filters may be mounted in compartment 125 without the use of an additional securing device.

[0033]FIG. 5 is a partial side view of a portion of polishing tool 100 showing polishing components located in processing compartment 106. During polishing, a semiconductor wafer 515 located in wafer holder 510 is pressed against pad 504 located on platen 505. During polishing, both platen 505 and wafer holder 510 are rotated. Also during polishing, a slurry is applied to pad 504 via dispense arm 305. Referring back to FIG. 1, processing compartment 106 includes three platens similar to those of platen 505.

[0034] Those of skill in the art will recognize that, based upon the teachings herein, several modifications may be made to the embodiments shown in FIGS. 1-5. For example, referring back to FIG. 3, the upstream and down stream transducers (e.g. 218 and 220) may be coupled to system controller 343 to provide indications of the measured pressures wherein controller 343 would cause those pressures to be displayed on display 339. In another example, controller 343 may be programmed to perform an operation based the receipt of the pressure differential information. For example, if the pressure differential information indicates that the usable state of the point of use filter has decreased to a replaceable level, controller 343 stops the wafer polishing by tool 100. Still in other embodiments, an indication that the pressure differential across the filter has exceeded a predetermined threshold, may be indicated by a light mounted on frame 101.

[0035] While particular embodiments of the present invention have been shown and described, it will be recognized to those skilled in the art that, based upon the teachings herein, further changes and modifications may be made without departing from this invention and its broader aspects, and thus, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. 

What is claimed is:
 1. A method for polishing a semiconductor wafer in a polishing tool, the method comprising: controlling by a flow regulator at a first location in a slurry path to a polishing pad, a flow rate of slurry to a polishing pad; filtering, with a point of use filter, the slurry at a second location in the slurry path located downstream of the first location; measuring a first pressure in the slurry path upstream of the filter; measuring a second pressure in the slurry path down stream of the filter; providing the slurry to the polishing pad; polishing the semiconductor wafer with the polishing pad; providing an indication including information based upon a pressure differential between the first pressure and the second pressure wherein the pressure differential is indicative of a usable state of the point of use filter.
 2. The method of claim 1, further comprising: calculating the pressure differential, wherein the information includes the pressure differential.
 3. The method of claim 2 further comprising: displaying the pressure differential.
 4. The method of claim 1, wherein the indication indicates that the pressure differential exceeds a predetermined threshold pressure.
 5. The method of claim 4 wherein the predetermined threshold pressure corresponds to the usable state of the filter being such that the filter needs to be replaced.
 6. The method of claim 4 further comprising: displaying an indication that the filter needs to be replaced in response to the indication indicating that the pressure differential exceeds a predetermined threshold pressure.
 7. The method of claim 6, further comprising: changing a filter used to filter the slurry in response to receiving the displayed indication.
 8. The method of claim 7 wherein the changing the filter includes snapping the filter into a notch in a bracket.
 9. The method of claim 1 further comprising: displaying the indication on a display.
 10. The method of claim 1 further comprising: providing the indication to a system controller of the polishing tool.
 11. A semiconductor wafer polishing tool comprising: a slurry path to provide slurry to a polishing pad; a flow regulator located in the slurry path and controlling the flow rate of the slurry to the polishing pad during polishing; a point of use filter located in the slurry path downstream from the flow regulator; a first pressure sensor located in the slurry path upstream from the point of use filter, the first pressure sensor measuring a first pressure and providing a first indication of the first pressure; a second pressure sensor located in the slurry path downstream from the point of use filter, the second pressure sensor measuring a second pressure and providing a second indication of the second pressure; and a pressure differential indicator coupled to receive the first indication and the second indication, the pressure differential indicator providing a third indication, the third indication including information based upon a pressure differential between the first pressure as indicated by first indication and the second pressure as indicated by the second indication, wherein the pressure differential is indicative of a usable state of the point of use filter.
 12. The polishing tool of claim 11, wherein the third indication includes a value of the pressure differential.
 13. The polishing tool of claim 11, wherein the pressure differential indicator further includes a display, the display displaying the third indication.
 14. The polishing tool of claim 13 wherein the third indication indicates that the filter needs to be replaced as based upon the pressure differential exceeding a predetermined threshold pressure.
 15. The polishing tool of claim 11, wherein the pressure differential further includes a controller operably coupled to receive the first indication and the second indication, wherein the controller calculates the pressure differential between the first pressure as indicated by first indication and the second pressure as indicated by the second indication wherein the third indication is based upon the pressure differential calculated.
 16. The polishing tool of claim 11, wherein the third indication includes an indication that the pressure differential exceeds a predetermined threshold pressure.
 17. The polishing tool of claim 16 wherein the predetermined threshold pressure corresponds to the usable state of the filter being such that the filter needs to be replaced.
 18. The polishing tool of claim 11, further comprising a system controller operably coupled to the pressure differential indicator to receive the third indication.
 19. The polishing tool of claim 18 further comprising a system display operably coupled to the system controller to receive information regarding the third indication for display on the system display.
 20. The polishing tool of claim 11, further comprising an isolation valve located in the slurry pathway downstream from the point of use filter, wherein the slurry travels through the isolation valve at a flow rate determined by the flow regulator.
 21. The polishing tool of claim 11 further comprising: a dispense arm located in the slurry path downstream from the point of use filter, wherein the dispense arm provides the slurry to the polishing pad.
 22. The polishing tool of claim 11, wherein the flow regulator includes a peristaltic pump.
 23. The polishing tool of claim 11, wherein the pressure differential indicator includes a display and a controller, wherein the controller is operably coupled to receive the first indication and the second indication, wherein the controller calculates the pressure differential between the first pressure as indicated by first indication and the second pressure as indicated by the second indication, wherein the display displays information based the pressure differential as calculated by the controller.
 24. The polishing tool of claim 11, further comprising a first pressure sensor includes a first pressure transducer and the second pressure sensor includes a second pressure transducer.
 25. The polishing tool of claim 11, further comprising: a frame, wherein the polishing pad is located within the frame and wherein the point of use filter is located within the frame.
 26. The polishing tool of claim 11 further comprising: a frame; a bracket mechanically coupled to the frame, the bracket including a notch sized to receive the filter in a snap-in configuration.
 27. A filtration system for a chemical mechanical polishing tool comprising: a slurry path having a first end to receive a slurry from a flow regulator and an second end for providing slurry for its application to a polishing pad for polishing, the slurry regulated at a flow rate by the flow regulator; a point of use filter located in the slurry path downstream of the first end; a first pressure sensor located in the slurry path upstream from the point of use filter, the first pressure sensor measuring a first pressure and providing a first indication of the first pressure; a second pressure sensor located in the slurry path downstream from the point of use filter, the second pressure sensor measuring a second pressure and providing a second indication of the second pressure; and the pressure differential indicator providing a third indication, the third indication including information based upon a pressure differential between the first pressure as indicated by first indication and the second pressure as indicated by the second indication, wherein the pressure differential is indicative of a usable state of the point of use filter.
 28. The system of claim 27, wherein the pressure differential indicator includes a display, the display displaying the third indication.
 29. The system of claim 28 wherein the third indication indicates that the filter needs to be replaced as based upon the pressure differential exceeding a predetermined threshold pressure.
 30. The system of claim 27, wherein the third indication includes an indication that the pressure differential exceeds a predetermined threshold pressure.
 31. The system of claim 30 wherein the predetermined threshold pressure corresponds to the usable state of the filter being such that the filter needs to be replaced.
 32. The system of claim 27, wherein the pressure differential indicator includes a display and a controller, wherein the controller is operably coupled to receive the first indication and the second indication, wherein the controller calculates the pressure differential between the first pressure as indicated by first indication and the second pressure as indicated by the second indication, wherein the display displays information based the pressure differential as calculated by the controller. 